The first time I ever tried this technique was with a film camera. I used a studio strobe in a bank place behind the drop and had to time the water drop by eye. Taking Polaroids verified the focus. I shot many rolls of film in the hope of capturing at least one successful image. It wasn't until the film came back from the lab the next day that I knew if I had been successful or not.
With digital cameras and digital timing devices, a shot like this is much easier today. You can determine immediately whether you are in focus and are correctly exposed, and can also see if your timing was accurate by looking at the back of your camera.